1. Technical Field of the Invention
The present invention relates in general to the field of telecommunications, and in particular, by way of example but not limitation, to side-tone control within a telecommunication instrument.
2. Description of Related Art
Conventional telecommunication instruments, such as wireline telephones, wireless or cordless phones and cellular handsets, typically employ a side-tone amplifier and associated circuitry that add a portion of an uplink signal produced by the microphone to a downlink signal received from a party at the far-end of a connection (xe2x80x9cfar-end partyxe2x80x9d) to generate an output signal supplied to the earpiece speaker (earphone). A purpose of the side-tone amplifier is to allow people to hear their own voices in an earphone and therefore compensate for the fact that at least one ear is completely or partially covered by an earphone. Without a side-tone amplifier, people may experience a loss of hearing while speaking into an instrument""s microphone, and as a result, may be unable to adequately control the volume of their voices due to inappropriate audio feedback.
Although a side-tone amplifier may enhance a user""s ability to communicate with a far-end party, the side-tone amplifier also introduces significant problems when the telecommunication instrument is operated in a noisy environment. In a typical configuration, a side-tone amplifier generates a side-tone signal based on the acoustic signals picked up by the microphone. Because the side-tone signal is combined with the downlink signal received from the far-end party to produce the output signal supplied to the earphone, the side-tone signal may significantly degrade the quality of the output signal. In a noisy environment, for example, background noise picked up by the microphone will be combined with the downlink signal. As a result, the background noise included in the side-tone signal may significantly decrease the signal-to-noise ratio of the output signal, and partially or completely mask the downlink signal.
Existing approaches have attempted to alleviate these problems by incorporating volume controls that enable a user to selectively control the output power of an earphone. The effectiveness of this approach, however, is limited by the quality and output power limitations of the earphone, and health considerations may further limit the effectiveness of this approach because a high volume output may damage the user""s hearing mechanism.
Other existing approaches utilize a gain control mechanism, which adjusts the gain of a side-tone amplifier in response to a detected power level of the uplink signal. For example, the gain control mechanism can decrease the gain of the side-tone amplifier in response to the power level of the uplink signal exceeding a predetermined threshold, and increase the gain of the side-tone amplifier in response to the power level of the uplink signal falling below a predetermined threshold. These approaches, however, adjust the gain of the side-tone amplifier based solely upon the power level of the uplink signal, and therefore fail to take into account other various side-tone control requirements that arise from a two-way conversation involving both an uplink signal and a downlink signal. Furthermore, the side-tone amplifiers employed in these existing approaches are configured with a fixed frequency response. Such a response prevents these approaches from further enhancing the quality and intelligibility of the output signal through adjustment of the side-tone amplifier""s frequency response so as to allow a user to better understand the speech signals received from a far-end party.
Therefore, in view of the significant deficiencies of existing approaches, there is a need for an approach that can more effectively provide side-tone control within a telecommunication instrument.
The deficiencies of the prior art are overcome by the method and apparatus of the present invention. For example, as heretofore unrecognized, it would be beneficial to provide side-tone control within a telecommunication instrument by measuring the energy of an uplink signal and the energy of a downlink signal, selecting amplifier parameters for controlling a transfer function of a side-tone amplifier based on the energy of the uplink signal and the energy of the downlink signal, and applying the amplifier parameters to the side-tone amplifier. The amplifier parameters can be selected to control the gain of the side-tone amplifier, the frequency response of the side-tone amplifier, or both the gain and the frequency responses of the side-tone amplifier based on the energy of the uplink signal and the energy of the downlink signal.
In one embodiment of the present invention, a side-tone control unit is configured to include a side-tone amplifier having a transfer function selectively controlled in accordance a set of amplifier parameters, and a side-tone controller, coupled to the side-tone amplifier, for selectively applying the set of amplifier parameters to the side-tone amplifier based on the detected energy of an uplink signal and the detected energy of a downlink signal. The side tone mechanism can also include a table of amplifier parameters that stores a plurality of sets of amplifier parameters, so that the side-tone controller can be configured to select the set of amplifier parameters from the plurality of sets of amplifier parameters by indexing the table in accordance with quantized values of the detected uplink signal energy and the detected downlink signal energy.
An important technical advantage of the present invention is that it enhances the quality and intelligibility of an output signal supplied to an earphone.
Another important technical advantage of the present invention is that it provides more effective side-tone control by taking into account the varying needs of side-tone control that occur during a two-way conversation.
Yet another important technical advantage of the present invention is the ability to significantly improve the signal-to-noise ratio of a downlink signal when the telecommunication instrument is operated in a noisy environment.
The above-described and other features of the present invention are explained in detail hereinafter with reference to the illustrative examples shown in the accompanying drawings. Those skilled in the art will appreciate that the described embodiments are provided for purposes of illustration and understanding and that numerous equivalent embodiments are contemplated herein.